1. Field of the Invention
The present invention relates generally to the field of forming connections and conducting links, and more particularly to forming connections and conductive links by directed thermal diffusion.
2. Discussion of the Background
It is known in the art to form interconnecting links between adjacent or closely situated conductive materials. In particular, in the semiconductor industry, it is necessary to form conductive links after an integrated circuit is formed in a number of applications. For example, because DRAM (dynamic random access memory) circuits sometimes contain manufacturing errors, they are often manufactured with extra rows and/or columns. When one row or column is found to be defective, a fuse is blown to disconnect the defective row or column and one of the extra rows or columns is connected in its place. The connection of the extra row or column is one example of an application wherein a conductive link must be formed. Another example of an application in which such links must be formed is certain types of programmable logic devices.
Several technologies are known for forming such conductive links. For example, anti-fuses are well known in the art. Other examples of forming such links are discussed in U.S. Pat. Nos. 5,940,727, 5,861,325, 5,585,602, 5,920,789 (all to Bernstein) and U.S. Pat. No. 4,810,663 (to Raffel et al.). In the Bernstein technique, the links are formed by heating a conductor separated from another conductor by a dielectric material such that the dielectric material fractures and melted metal flows in fissures formed by the fractured dielectric material to connect the conductors. In the Raffel technique, conductive layers are separated by a material which forms an alloy with the conductive materials when heated by a laser.
There are drawbacks to all of the foregoing links, including, but not limited to, use of non-standard processing steps, low conductivity, potential of damage to surrounding area, and/or the requirement of directing a laser beam at the exact location where an interconnecting link is desired.
The present invention provides a method for forming a conductive link using a process referred to herein as directed thermal diffusion wherein energy is applied to a conducting body that includes portions with differing thermal mass, with the energy being applied in a portion of the conducting body with relatively higher thermal mass, resulting in a thermal diffusion front directed toward a portion of the conducting body with lower thermal mass. The lower thermal mass portion is surrounded by non-conducting material, while the higher thermal mass portion may or may not be surrounded by non-conducting material. The lower thermal mass portion then expands, thereby creating fissures in the surrounding non-conducting material. Next, the lower thermal mass portion melts and flows through the fissures until contact with another conductor is made, thereby forming a conductive link between the conducting body and the other conductor. In preferred embodiments, relative motion between the conducting body and the energy source is created such that the energy source moves toward the lower thermal mass portion, thereby creating an enhanced thermal diffusion front in the direction of the lower thermal mass portion.